The present invention relates to a golf ball and more particularly to an improvement in a in the dimple pattern of the golf ball.
A golf ball has approximately 200 to 550 dimples on the surface thereof. The role of the dimples resides in one aspect in that such dimples disturb the air stream around the golf ball during the flight to accelerate the transition of turbulent flow at the boundary layer of the golf ball, thereby causing turbulent flow separation (which will be hereinafter referred to as a “dimple effect”). The acceleration of the transition of the turbulent flow causes a separating point of the air from the golf ball to be shifted backward so that the drag coefficient (Cd) is reduced, resulting in an increase in the flight distance of the golf ball. Moreover, the acceleration of the transition of the turbulent flow increases the differential between upper and lower separating points of the golf ball which is caused by back spin. Consequently, a lift action on the golf ball is increased.
There have been proposed various golf balls having improved dimple patterns in order to enhance a flight performance. For example, Japanese Patent Publication No. Sho 58-50744 (U.S. Pat. No. 5,080,367) has disclosed a golf ball in which dimples are densely provided such that a that the pitch between the dimples is 1.62 mm or less, if possible. Japanese Laid-Open Patent Publication No. Sho 62-192181 (U.S. Pat. No. 4,813,677) has disclosed a golf ball in which dimples are densely provided so as not to form a new dimple having an area which is equal to or larger than the mean area in the land portion other than the dimples. Japanese Laid-Open Patent Publication No. Hei 4-347177 (U.S. Pat. No. 5,292,132) has disclosed a golf ball in which dimples are densely provided such that the number of land portions in which a rectangle having a predetermined dimension can be drawn is 40 or less.
All the golf balls disclosed in the known publications have densely provided dimples, in other words, the surface area occupation ratio of the dimple is increased. Those skilled in the art have recognized that the surface area occupation ratio is one of important elements which influence the dimple effect.
However, the surface area occupation ratio is not the only index which relates to the dimple effect. In this respect, in addition to the surface area occupation ratio, there is room for investigating other areas for further enhancing flight performance.